The present invention relates to the field of mass storage devices. More particularly, this invention relates to a disc drive which includes a ramp for loading and unloading read/write heads from the surface of a disc in the disc drive.
One of the key components of any computer system is a place to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations over the disc from track to track, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically housed within a small ceramic block. The small ceramic block is passed over the disc so that it can read information representing data from the disc or write information representing data to the disc. When the disc is operating, the disc is usually spinning at relatively high revolutions per minute (xe2x80x9cRPMxe2x80x9d). These days common rotational speeds are 7200 RPM. Rotational speeds in high performance disc drives are as high as 10,000 RPM. Higher rotational speeds are contemplated for the future. These high rotational speeds place the small ceramic block in high air speeds.
The small ceramic block, also referred to as a slider, is usually aerodynamically designed so that it flies over the disc. The bottom side of the slider, the area that is facing the disc surface, is aerodynamically designed so that the distance variation (fly height variation) of the head to the disc is minimal. Fly height variations occur, because of different shew angles between the air flow and the slider leading edge and different air speeds, while the slider is positioned on different tracks on the disc. The slider has an air bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. The air bearing surface is that portion of the slider that is nearest the disc as the disc drive is operating. When the disc rotates, an air bearing is formed between the disc and head. This air bearing lifts the head off of the disc and reduces friction forces. Some head designs have a depression in the air bearing surface that produces a negative pressure area at the depression. The negative pressure or suction counteracts the pressure produced at the rails to provide more uniform fly heights from disc inner diameter (ID) to outer diameter (OD). The fly height is the thickness of the air lubrication film or the distance between the disc surface and the head. This film eliminates mechanical friction and resulting wear that would occur if the slider and disc were in mechanical contact during disc rotation.
The best performance of the disc drive results when the head is flown as closely to the surface of the disc as possible without contact between the disc and the slider. Today""s slider is designed to fly on a very thin layer of gas or air. In operation, the distance between the head and the disc is very small. Currently xe2x80x9cflyxe2x80x9d heights are about 1-2 microinches. It is contemplated that in future disc drives, the slider will not fly on a cushion of air but rather will pass through a layer of lubricant on the disc. A flexure or gimbal is attached to the load spring or load beam and to the slider. The flexure allows the slider to pitch and roll so that the slider can remain in close proximity to the disc.
Information representative of data is stored on the surface of the memory disc. Disc drive systems read and write information stored on tracks on memory discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the memory disc, read and write information on the memory discs when the transducers are accurately positioned over one of the designated tracks on the surface of the memory disc. The transducer is also said to be moved to a target track. As the memory disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the memory disc. Similarly, reading data on a memory disc is accomplished by positioning the read/write head above a target track and reading the stored material on the memory disc. To write on or read from different tracks, the read/write head is moved in a substantially radial direction across the tracks to a selected target track. To be totally accurate, the slider passes in a circular motion as it pivots about the axis of the actuator assembly. The data is divided or grouped together on the tracks. In most disc drives, the tracks are a multiplicity of concentric circular tracks. Servo feedback information is used to accurately locate the transducer.
One of the most critical times during the operation of a disc drive occurs just before the disc drive shuts down or during the initial moment when the disc drive starts. When shutdown occurs, the slider fly height decreases until the slider contacts the disc. The small block or slider is moved to a non-data area of the disc where it literally landed and skidded to a stop. To improve magnetic performance, discs now are formed with a smooth surface. The smooth surface allows lower flying heights. Stiction, which is static friction, occurs between the air bearing surface of the slider and the smooth disc surface. Forces from stiction, in some instances, can be high enough to separate the slider from the suspension or prevent the disc from spinning.
To overcome the stiction problem and to provide for a much more rugged design for disc drives used in mobile computers, such as portable computers and notebook computers, disc drive designers began unloading the sliders onto a ramp positioned on the edge of the disc. Disc drives with ramps are well known in the art. U.S. Pat. No. 4,933,785 issued to Morehouse et al. is one such design. Other disc drive designs having ramps therein are shown in U.S. Pat. Nos. 5,455,723, 5,235,482 and 5,034,837. Before power is actually shut off, the actuator assembly moves the suspension, slider and transducer to a park position on the ramp. Commonly, this procedure is referred to as unloading the heads. The disc drive must also be able to unload the heads if a so-called hot unplug occurs, where the slider is moving at full speed towards inner diameter (xe2x80x9cIDxe2x80x9d) and has almost reached the ID. The rotary inertia of the disc stack is now used to spin the motor, which is used as a generator to move the head stack from the ID to the outer diameter (xe2x80x9cODxe2x80x9d) and up the ramp. Unloading the heads helps to insure that data on the disc is preserved since, it prevents shock inputs from causing heads to lift off of the disc and slap back down onto the disc. Unloading the heads can also prevent disc-to-arm contact that can cause disc damage. When starting up the disc drive, the process is reversed. In other words, the suspension and slider are moved from the ramp onto the surface of the disc which is already spinning at a constant speed. This is referred to as loading the heads or sliders onto the disc.
Use of a ramp to load and unload the disc overcomes many aspects of the stiction problem. However, during the loading process and the unloading process, the slider can contact the disc and result in head or disc damage. The danger of contact between the slider and discs is fairly high.
Dynamic load/unload of the slider to and from the disc is a very critical process, because of the potential danger of contact between the disc and the slider air-bearing surface. Since the air-bearing suction exerts a force that will hold the slider on the disc during the unloading process, deformation energy is stored in the lift tab and gimbal as the lift tab moves up the ramp. When the ramp induces sufficient lift force on the head, the head will release from the disc. This release of the head from the disc dissipates the air bearing and allows the energy stored in the lift tab and gimbal to be released. This stored potential energy is converted into kinetic energy similar to the conversion that occurs when a spring is pulled and then released. The head suspension system will oscillate in a manner similar to the simple spring mass system. The period of this vibration depends on the system""s stiffness and natural frequency when the lift tab is on the ramp. A lower natural frequency will increase the time before the slider bounces back which gives more time to move the head clear of the disc and therefore allow slower unload velocities. However, low natural frequency systems have low lift tab stiffnesses and low stiffnesses mean increased lift tab deflections that result in an increased unload footprint or increased distance required to unload the head. A stiff system would have a small unload footprint but will also have a higher natural frequency. A stiff lift tab with its higher frequencies, will cause the slider to bound back more quickly. The lower natural frequency is desirable but with a stiff lift tab.
What is needed is a disc drive having a structure that allows for use of a stiff lift tab but which has a lower resonant frequency so that the initially lifting off of the slider can take place over a longer amount of time. Also needed is a disc drive in which the time required to move the lift tab up a selected distance on the ramp is less than one cycle of the natural resonant frequency of the actuator assembly. This will prevent the slider from rebounding and slapping the disc. What is also needed is a method for loading the sliders onto the disc without causing damage to the heads and discs. Also needed is a method for avoiding contact between the disc and the slider so that the damage resulting from a contact will be minimal or even eliminated. The system should be robust and easy to manufacture.
A magnetic disc drive includes a base, a rotating disc attached to the base, and a ramp attached to the base near said disc. The magnetic disc drive also has an actuator assembly attached to the base. The actuator assembly rotates about an actuator pivot point. The actuator assembly further includes a suspension attached to one end of the actuator assembly, and a transducer attached to the suspension. The actuator assembly moves the transducer between data tracks on the disc and an unload position. The suspension includes a lift tab which contacts the ramp at a contact point as the transducer is moved to the unload position. As the actuator assembly moves the transducer to the unload position, the contact point between the lift tab and the ramp moves toward the actuator pivot point. The lift tab contact point movement towards the pivot is caused by the ramp edge angling towards the actuator pivot point. The lift tab contact point on the ramp moves towards the actuator pivot point as the lift tab moves up the ramp. The lift tab contact point on the ramp may follow a straight or contoured path. As the lift tab contact point moves closer to the actuator pivot point, its reduction in its effective length causes its natural frequency to increase.
The natural resonant frequency of the actuator assembly when the lift tab contacts the ramp near the disc may be selected to optimize any of the following conditions: 1) its natural frequency with regard to disc RVA components, 2) head bound back period, and 3) increased compliance to accommodate effects of tolerances. The lift tab contact point changes as the heads move out of the flyable zone of the disc. The lift tab contact point is selected to increase the lift tab stiffness to ensure that all of the heads are off of the discs when assembly tolerances are considered. While flying over the disc, the initial cycle time of the actuator arm may be selected to be a longer time, but since the resonance frequency increases as the lift tab moves along the ramp, the cycle time of the actuator arm effectively decreases.
Also disclosed is an information handling system which includes a base, a disc rotatably attached to the base, a ramp attached to the base near the disc, and an actuator assembly pivotably attached to the base. The actuator assembly pivots about an actuator pivot point. The actuator further includes a suspension attached to one end of the actuator assembly, and a slider carrying the read/write element attached to the suspension. The dimple is part of the load beam. It is either formed or partially etched. The dimple is a pivot point about which the slider attached to the flexure or gimbal pivots. The gimbal is a usually very compliant sheet metal structure that is welded to the load beam. The slider is then glued to the flexure or gimbal. The actuator assembly moves the slider between a transducing position and an unload position. The suspension includes a lift tab which contacts the ramp at a contact point as the transducer is moved to an unload position. The ramp is designed so that the distance between the contact point and the actuator pivot point shortens as the actuator assembly moves the transducer up the ramp. The actuator assembly resonant frequency increases as the distance between the contact point and the actuator pivot point shortens. The lift tab contact edge may be substantially straight and positioned on a radial or non-radial chord of the disc or may be substantially curved. The ramp further comprises a lift tab contact edge where the lift tab contacts the ramp. The lift tab contact point moves toward the actuator pivot point as the actuator assembly moves the transducer up the ramp toward the unloaded position.
Also disclosed is a disc drive which includes a disc, an actuator assembly, a transducer attached to the actuator assembly, and a device for moving the transducer between a data track with respect to the disc and an unloaded position.
Advantageously, the invention allows for use of a stiff lift tab that has a lower resonant frequency at the bottom of the ramp so that the initial lift off of the slider can take place over a longer time. The resonant frequency increases as the lift tab moves further up the ramp which results in minimization of the footprint during unloading. The length between the contact point on the slider and the pivot point of the actuator shortens as the lift tab moves up the ramp. Initially, the time required to move the lift tab up a selected distance on the ramp is less than one cycle of the natural resonant frequency of the actuator assembly. This method for unloading the sliders from the disc prevents or minimizes the possibility of contact as well as the possibility of damage to the heads. The ramp features required for this design are easy to manufacture and the ramp does not require adjustment.